The 'ping' was recorded at a frequency being emitted at 37.5kHz, the same frequency as a black box device, according to Chinese news agency Xinhua.

Then the ship Haixun 01 're-detected' the signals for 90 seconds withing just 2km of the original detection - according to chief coordinator Angus Houston.

He told a press conference: "This morning we were contacted by the Chinese authorities and advised that Haixun 01 had late yesterday afternoon re-detected the signals for 90 seconds within just 2km of the original detection. This is an important and encouraging lead but one which I urge you to continue to treat carefully."

"Obviously we take any reported leads in the search very seriously that is why today Royal Australian Air Force assets were deployed to assist in further examining the acoustic signals in the vicinity of the Chinese ships."

"Speculation and unconfirmed reports can see the loved ones of the passengers put through terrible stress and I don't want to put them under any further emotional stress at this very difficult time."

Malaysia said earlier on Saturday it had begun a formal investigation into the jet’s March 8 disappearance that would comprise experts from around the world, while the huge hunt for the Boeing 777 airliner intensified in the Indian Ocean.

Normally, a formal air safety investigation is not launched until wreckage is found.

But there have been concerns that Malaysia’s informal investigations to date have lacked the legal standing of an official inquiry convened under U.N. rules.

Authorities have not ruled out mechanical problems as a cause but say the evidence, including the loss of communications, suggests Flight MH370 was deliberately diverted thousands of kilometres (miles) from its scheduled route.

Defence and acting Transport Minister Hishammuddin Hussein told a news conference that Australia, China, the United States, the United Kingdom and France had agreed to send representatives to take part in the investigation.

The extensive search and rescue operation has so far included assets from around 26 countries.

Under International Civil Aviation Organisation rules, the country where the aircraft is registered leads the investigation when the incident takes place in international waters.

A spokesman from the U.N. agency told Reuters that it received official notification of the accident on 28 March, meaning that the investigation was considered officially launched on that date.

Hishammuddin said that the investigation would be made up of three groups:

- An "airworthiness" group would examine maintenance records, structures and systems

- An "operations" group would study flight recorders, operations and meteorology

- A "medical and human factors" group would look into psychology, pathology and survival factors

The Malaysian government has also set up ministerial committees to oversee everything pertaining to the next of kin of the passengers and crew on board the aircraft, the appointment of the investigation team and the deployment of assets in the search operation.

The Malaysia Airlines chief executive said the airline’s role was to take care of the families of passengers who were on its missing jetliner and that it had curbed its advertising out of respect for their well-being.

Malaysia Airlines and the Malaysian authorities have faced heavy criticism, particularly from China, for mismanaging the search and holding back information.

Most of the 239 people on board the missing flight MH370 were Chinese.

Chief Executive Ahmad Jauhari Yahya said it was "beyond any reasonable doubt the aircraft was lost".

On Monday, it will be 30 days since the jetliner lost communications and disappeared from civilian radar.